Description: The proposed study, a secondary analysis of Medicare and Medicaid databases in New Jersey from the years 1987-1994, will analyze utilization patterns of ESRD patients in the year prior to hemodialysis or transplantation. In addition to analyzing claims data, the study will abstract primary medical records to obtain greater clinical detail. The aims of the research are: (1) to study nephrologist services in the year prior to hemodialysis/transplant (HD/Tx); (2) to study use of specialist care variables by age, gender, socio-economic status, and race during the year prior to HD/Tx; and (3) to determine whether the referral patterns in the year prior to HD/Tx are associated with outcomes in the year after Hd/Tx. The study focuses on the timing and follow-up care provided by the nephrologist. It will examine: (1) how use of a nephrologist varies by patient characteristics (age, gender, socioeconomic status, and race) and primary care provider characteristics; (2) how the use of a nephrologist referral affects the clinical course of the disease and outcomes (mortality, rates of hospitalization, frequency of vascular access procedures and blood transfusion), adjusting for co-morbidities; (3) whether different measures of case mix will yield different results; and (4) the use of specialty services and health care costs.